Fracture reasons of nuclear grade manual stop valve stem in nuclear power plant

The valve stem of a nuclear grade manual stop valve in a nuclear power plant fractured during operation. The fracture reasons of the valve stem were studied using methods such as macroscopic observation, chemical composition analysis, mechanical property testing, metallographic examination, scanning electron microscopy and energy spectrum analysis, and filler analysis. The results show that the improper control of the heat treatment process of the valve stem resulted in a deterioration of the corrosion resistance of the valve stem. During operation, the filler in contact with the valve stem had a high content of corrosive elements. Under long-term high tensile stress, the valve stem experienced stress corrosion fracture.